Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 18 2024 08:23:39 FOUS30 KWBC 180823 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 323 AM EST Wed Dec 18 2024 Day 1 Valid 12Z Wed Dec 18 2024 - 12Z Thu Dec 19 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PARTS OF THE=20 OHIO AND TENNESSEE VALLEYS ALONG WITH THE SOUTHEAST FLORIDA COAST... ....Parts of the Mid-South to Lower Ohio Valley...=20 Maintained the Marginal Risk area across parts of western and central Tennessee into southern Kentucky as models still advertise an=20 upper-level trough amplifying to the west which allows for a more=20 curved upper level jet streak on the lee side of the trough. That=20 configuration may result in some enhanced rainfall rates...an idea=20 supported by the 18/00Z HREF neighborhood probabilities showing=20 potential for rainfall rates exceeding an inch per hour between=20 12-18Z today (mainly in Tennessee). With rainfall blossoming to=20 the west of the outlook area in the pre-dawn hours this morning=20 helping to prime the soils a bit more and a general slowing of the=20 eastward progression across the Tennessee Valley compared with=20 earlier forecasts...opted to extend the Marginal risk area a bit=20 farther westward than previously indicated. The HREF probability of exceeding flash flood guidance remained low but did reflect=20 somewhat higher probabilities west of the same guidance from the=20 17/12Z and 17/18Z runs. The decision to expand westward slightly=20 was also driven by the observed rainfall during the past day or two over parts of northwest Tennessee and southwest Kentucky which has resulted in the latest 1-hour and 3- hour flash flood guidance=20 coming down and the 0-40km soil moisture percentiles per NASA SPoRT have climbed to 60-80% for most areas.=20 ....Southeast FL...=20 Post frontal easterly low level flow off the Atlantic will linger=20 allowing for a possible repeat of convective clusters over and=20 near the southeast Florida coastline today. The 00Z runs of the=20 high-res CAMs continued to show onshore low-level moisture=20 flux/convergence and sufficient deep-layer instability to support=20 localized downpours. The 18/00Z HREF supports rates of 2+ inch per=20 hour peaking around 10 percent during the afternoon with and a=20 50-70 percent 40km neighborhood probabilities of at least 5 inches=20 of additional rain and 30-50 percent probabilities of 8+ inches.=20 Given that these numbers are comparable with the 17/12Z and 17/18Z=20 runs of the HREF...saw little reason to make too many changes other than nudges to the boundary of the previously issued Marginal risk area.=20 Bann Day 2 Valid 12Z Thu Dec 19 2024 - 12Z Fri Dec 20 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 3 Valid 12Z Fri Dec 20 2024 - 12Z Sat Dec 21 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_VGHg43JVbddWsGyChhnr8-fx97u_pymZDz3gX1SY7Kd= dlOcg__DFsi6EXZOzhmDQhXigylvL1PrE30Ftfyc_-3_3qM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_VGHg43JVbddWsGyChhnr8-fx97u_pymZDz3gX1SY7Kd= dlOcg__DFsi6EXZOzhmDQhXigylvL1PrE30Ftfycs51r0AU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_VGHg43JVbddWsGyChhnr8-fx97u_pymZDz3gX1SY7Kd= dlOcg__DFsi6EXZOzhmDQhXigylvL1PrE30FtfycVJoHKhQ$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .